1. Field of the Invention
The present invention relates to a camera device comprising a lens unit and a camera body. In particular, it relates to a camera device which can properly manage an accumulated exposure time of each image sensor and accurately determine a deterioration level of the image sensor according to actual usage environment, as well as to a lens unit and a camera body constituting such a camera device.
2. Description of the Related Art
A single lens reflex digital camera is well known for a type of lens interchangeable camera devices. It generally incorporates an image sensor in a camera body in which a photographic lens is mounted. However, one having an image sensor in a lens unit is also known (disclosed in Japanese Patent Application Publication No. 2008-98818, for example).
A camera device having an image sensor in a camera body has an advantage of cost reduction since the number of mountable image sensors is one. Meanwhile, a camera device having an image sensor in a lens unit has an advantage of extensibility since a lens unit including an optimal, most advanced image sensor can be used and at the same time another image sensor can be also mounted in a camera body.
In capturing a subject image with a digital camera or previewing the image on a display of the camera body, a shutter is open. An image sensor is exposed to ambient light with the shutter open, that is, not only during a shooting operation but also during turning-on of the power source.
The image sensor (photo transistor, for example) is sufficiently tolerative to exposure, however, a color filter attached to the front of the image sensor is not and it degrades due to exposure over time (disclosed in Japanese Patent Application Publication No. 2000-183322, for example). Color degradation of the color filter causes the color of a captured image to blur and deteriorates the image quality.
For prevention of this problem, it is a good way to detect degradation of the color filter before the degradation is advanced over a certain level and notify a user of the degradation and time for replacement. A type of digital camera incorporating an image sensor in a camera body can relatively easily count accumulated exposure time of the image sensor to determine when the image sensor should be replaced. To the contrary, another type of digital camera incorporating an image sensor in a lens unit needs to distinctly store accumulated exposure time of each lens unit (each image sensor) for determining the time for replacement in the camera body. To perform such data management and storage, it is necessary for the camera body to comprise sufficient memory areas and function. Moreover, further contrivances are required to distinctly manage and store accumulated exposure times of different lens units which include the same image sensors.
Another problem is that since an operative element as keys or a display unit as an LCD is mounted in the camera body irrespective of the type of a lens unit, the camera body has to comprise a function to manage and process information on each image sensor and to notify degradation of the color filter and display the notification. However, there is no prior art technique or device which deals with such a problem.
Furthermore, amount of light incident on the image sensor changes depending on a photographic condition so that it is not possible to accurately determine degradation of the image sensor simply from stored accumulated exposure time. Prior art techniques fail to address how to accurately determine degradation of the image sensor.